The goal is to measure the dimensions of the human photoreceptor mosaic, and to describe the impact of the mosaic on spatial vision in different parts of the visual field. A psychophysical technique will be developed to measure the packing arrangement, spacing, and size of cones across the central retina. This noninvasive technique exploits the appearance of moire patterns formed between fine interference fringes and the cone mosaic to deduce the structure of the mosaic in the living eye. The results of the moire technique will be validated with results from an improved anatomical technique, that will allow measurements of the dimension of the human cone mosaic with minimum histological artifact. The quantitative description of the human cone mosaic derived from the psychophysical and anatomical results will be used to construct a model of the first stages of spatial vision. In addition to the photoreceptor mosaic, the model will incorporate the optical quality of the eye and neural spatial filtering, and will predict the spatial performance of the visual system at each retinal eccentricity. These predictions will be compared with acuity and contrast sensitivity measurements made with interference fringes, to provide a clearer understanding of the limitaitons imposed ;by the first stages of the visual system on pattern vision.